Alar, transverse, and apical ligament strain due to head-turned rear impact.

STUDY DESIGN: Determination of alar, transverse, and apical ligament strains during simulated head-turned rear impact.

OBJECTIVES: To quantify the alar, transverse, and apical ligament strains during head-turned rear impacts of increasing severity, to compare peak strains with baseline values, and to investigate injury mechanisms.

SUMMARY OF BACKGROUND DATA: Clinical and epidemiologic studies have documented upper cervical spine ligament injury due to severe whiplash trauma. There are no previous biomechanical studies investigating injury mechanisms during head-turned rear impacts.

METHODS: Whole cervical spine specimens (C0-T1) with surrogate head and muscle force replication were used to simulate head-turned rear impacts of 3.5, 5, 6.5, and 8 g horizontal accelerations of the T1 vertebra. The peak ligament strains during impact were compared (P < 0.05) to baseline values, obtained during a noninjurious 2 g acceleration.

RESULTS: The highest right and left alar ligament average peak strains were 41.1% and 40.8%, respectively. The highest transverse and apical ligament average strain peaks were 17% and 21.3%, respectively. There were no significant increases in the average peak ligament strains at any impact acceleration compared with baseline.

CONCLUSIONS: The alar, transverse, and apical ligaments are not at risk for injury due to head-turned rear impacts up to 8 g. The upper cervical spine symptomatology reported by whiplash patients may, therefore, be explained by other factors, including severe whiplash trauma in excess of 8 g peak acceleration and/or other impact types, e.g., offset, rollover, and multiple collisions.